DESCRIPTION (adapted from the application) Disproportionate numbers of alcohol and drug users are infected with Hepatitis C virus (HCV). Although the majority of new cases appear to result from sharing contaminated drug paraphernalia, approximately 20% are attributed to sexual contact with an infected person. However, the HCV infectivity of semen and saliva is controversial. Based on evidence that alcohol and drug use are associated with high-risk sexual behavior (e.g., multiple sexual partners, a history of sexually transmitted diseases, and anal sex), violent behavior, and accidental injuries, we postulate that: 1) heavy drinking and other drug use increase HCV transmission via blood-to-blood contact in the context of sexual and other intimate interactions by promoting exposure to menstrual blood and bleeding caused by minor and major trauma and 2) heavy alcohol consumption may promote HCV transmission by depressing the immune system, increasing serum HCV RNA levels. We propose to assess lifetime and current drinking patterns, other drug use, and alcohol/drug-related behavior associated with possible blood-to-blood contact in the context of sexual, intimate situations in 16 STD clinic clients, 400 positive for anti-HCV and 1200 negative. Serum levels of HCV RNA will be assessed in anti-HCV+ clients by polymerase chain reaction. The relations between-alcohol/drug use and HCV status and the potential mediating effects of blood-to-blood contact related to high-risk sexual behavior, sexual victimization, domestic and other violence, accidental injuries, and unsafe drug use will be investigated us hierarchical regression analytic techniques; interaction terms will be used to investigate gender and racial differences in these relations. Cluster analysis will be employed to identify behavioral typologies associated with HCV status. Finally, the influence of lifetime and current drinking patterns on serum HCV RNA levels will be investigated, taking into account the effects of diet, smoking, and concomitant infections.